1. Field of the Invention
This invention pertains to improvements in downhole flow control valve actuation and particularly to a method and an apparatus for actuating valves using the changes in fluid pressure within the tool string to change the valve positions from drilling to mining while in the borehole.
2. Description of the Prior Art
Hydraulic borehole mining of ore is broadly known in the art as evidenced by the following United States Patents:
U.S. Pat. Nos. 3,155,177 and 3,316,985 issued to A. B. Fly on Nov. 3, 1964 and May 2, 1967 respectively teach a method and apparatus for slurry mining through a borehole which may be changed between its drilling mode of operation and its mining mode of operation to mine several different strata without removing the tool from the borehole. The drill string is equipped with a conventional drill bit enabling the machine to drill through hard formations; the drill bit being driven by a hydraulic drilling device. The invention teaches the essential controls needed to convert from drilling to mining, i.e., mining nozzle flow, eductor nozzle flow and fluid flow to the drill bit each with a drilling mode and a mining mode of operation. Electric motors within the tool string operate the valves to convert the apparatus from the drilling mode to the mining mode of operation while the tool is still in the borehole.
U.S. Pat. Nos. 3,730,592 issued May 1, 1973 and 3,747,696 issued July 24, 1973 to Wenneborg et al discloses a method and apparatus for borehole mining wherein a hydraulic actuating force for changing the function of the tool from drilling to mining is transmitted from the surface and the actuating fluid line is located wholly within the fluid supply passage to the lower tool section; the hydraulic valve operating means is used to operate the mining nozzle, foot valve and a slurry eductor located at the base of the tool.
U.S. Pat. No. 4,035,023 filed July 15, 1975 and issued July 12, 1977 to Clifford Cockrell discloses the use of a rotatable concentric dual-conduit tool string with Hydril type screwed joints wherein fluid is directed down the annular space between the conduits and the slurry is returned to the surface through the inner conduit. The cavity is subjected to air pressure sufficient to raise the slurry to the surface via the slurry discharge conduit. A foot valve controls the volume of slurry rising to the surface and is hydraulically operated by the differential pressure the vented cavity pressure at the base of the tool and the hydraulic pressure supplied by a slurry level controller.
In this disclosure Cockrell is the first to teach a principle of self-activating down-hole hydraulic valves for tool control; he is first to disclose, describe and use the differential pressure between a control pressure equivalent to or less than system pressure and the vented cavity pressure to establish a hydraulic actuating force for down-hole hydraulic valve control. Cockrell is also first to teach, describe and use the differential hydraulic actuating force between a control pressure and the cavity pressure to modulate down-hole control valves.
U.S. Pat. No. 4,059,166 of Nov. 22, 1977 and No. 4,067,617 of Jan. 10, 1978 issued to P. R. Bunnelle disclose a apparatus for slurry mining wherein several different hydraulic control systems are disclosed to convert the down-hole tool from drilling to mining all with valve control means located within the fluid supply passage of the tool. A control system employing a conduit extending to the surface is used to hydraulically modulate the eductor nozzle to control the cavity pressure; control systems activated by the difference between the pump pressure and a vented or cavity pressure are also employed. Self-activating systems to modulate the eductor nozzle also employ the pressure difference between a control pressure and a vented cavity pressure for valve actuation. Seperate control systems are employed for the eductor and the foot valve. An important feature of these systems is that the valve actuating control pressure and the drilling pressure are the same during drilling while during mining the valve actuating control pressure is established by venting to the cavity pressure or to the atmosphere.
U.S. Pat. No. 4,077,671 of Mar. 7, 1978 and No. 4,077,481 of Mar. 7, 1978 issued to P. R. Bunnelle discloses a modified valve control system which is self-activating by responding to the pressure differential between the system pressure and the pressure in the well cavity. In this disclosure the valve control means is responsive to fluid pressure differences; the control means having a system pressure end and a vented "control end". The mining nozzle includes a mining nozzle, seat and a mining nozzle cylinder slideable receiving the nozzle plug which receives system pressure at a system end and a control pressure at a control end. The eductor nozzle cylinder and foot valve also have a control end which is "vented" during mining. Venting to the atmosphere is also used as a control means. A "vented" control fluid is supplied for selectively opening or closing valves which acts in opposition to the fluid at system pressure on the control means to change the tool function. The salient feature of this method is that during the drilling mode the valve actuating control pressure and the drilling pressure are the same while during mining the valve actuating control pressure is established by venting to the cavity pressure or to the atmosphere.